(19873) Add OS major release fact

On RHEL clones and Debian (Amazon, CentOS, CloudLinux, Debian, Fedora,
OEL, OracleLinux, OVS, RedHat, Scientific, SLC) it would be useful to
pull out the major release version

ie 5.8=>5, 6.3=>6, 6.0.3=>6

This is available as the lsbmajdistrelease but there are too many
dependencies on LSB for minimal installs
Merge branch 'pull-411' into 1.7.x
Merge branch '1.7.x'